This invention relates to a throw-away insert having a chip breaker effecting an improved disposal of chips from a machined surface.
With an increasing tendency toward unmanned machining, the importance of chip disposal is increasing. Namely, because the depth of cut is small in finish cutting, the chips tend to be long. Such chips may make it difficult for a robot hand to attach and detach tools and workpieces or may clog a conveyor, thereby hampering the unmanned operation.
But it is not easy to eliminate such difficulties because in finish cutting, the requirements for the surface roughness and dimensional accuracy are very high.
For example, if priority is given to breaking chips, there is known a method of forcibly cutting and breaking chips by providing the breaker wall as near to the tip of the cutting edge as possible. But in such a case, the material machined develops so-called "plucking" and chattering, thereby lowering the surface roughness. Also, because of increased cutting resistance, the dimensional accuracy as well as the tool life are diminished.
As will be apparent from the above discussion, in the unmanned finish cutting operation, it is necessary to solve the above-described two problems simultaneously. But this requirement cannot be met by any of the conventional chip breakers used in finish cutting such as small-diameter boring, e.g. the breakers shown in FIGS. 9a and 9b and in FIGS. 10a to 10c, and the breakers shown in FIGS. 11a and 11b having a groove formed by a die so as to extend all the way around thc insert.
If it is impossible to break chips, the best way to dispose of the chips is to curl them into as small of pieces as possible and stably discharge them in such a direction as not to become tangled.
In this respect, the conventional breakers shown in FIGS. 9 and 11 are not desirable because they cannot forcibly discharge chips in a predetermined direction and thus the direction in which the chips flow after clearing the breaker tends to be unpredictable.
The breaker shown in FIG. 10 does produce a chip guiding effect because a breaker groove 4 is defined by a surface inclined downwardly toward front cutting edge 2 at an angle .THETA.. But because the strength of the breaker at edge 2 tends to drop with an increase in the angle .THETA., the maximum allowable value for .THETA. is rather small. Thus it is difficult to reliably control the flow of chips.